The invention relates to a lifting hook comprising a hook body with a hook stem and a hook tip; a safety latch with a fastening end and a free latch end, the fastening end of the safety latch being pivotably fastened close to the hook stem so as to move the safety latch between an open position and a closed position, the safety latch being in its open position substantially against the inside of the hook body in a position that leaves a hook jaw free, while in the closed position of the safety latch the latch end extends across the hook jaw to the hook tip and against it, resting against the inside of the hook body and its jaw, closing the jaw; and means for actuating the safety latch, the means comprising a spring arranged between the safety latch and the hook body and forcing the latch end into the closed position, and a locking and releasing device for locking the safety latch into the open position and for releasing the safety latch from the open position. The invention also separately relates to a safety latch to be attached to existing hooks, the safety latch being of the above-described type, and to a locking and releasing device of the lifting hook safety latch that can be mounted on existing safety latches that are also of the above-described type.
The purpose of a safety latch for a lifting hook is to prevent the load of a crane from falling during the use of the crane and to assist a user of the lifting hook of the crane to load and unload the hook safely and efficiently. The loading of the hook naturally refers to fastening a load to the hook and the unloading, correspondingly, to releasing the load from the hook. Safety and efficiency are considerably increased if the user is able to use both hands at the same time for releasing the load.
In known hooks, the safety latch is typically pressed open against a spring force pushing the safety latch closed, and kept in the open position with one hand. This prevents the use of the other hand for releasing the load as the hand must be used for keeping the safety latch open all the time when the load is being released. Moreover, opening the safety latch of large hooks and keeping it open requires a lot of force. Hence the load is very difficult to release and often another person is needed to keep the safety latch open. There is also a risk of hands or fingers getting caught between the safety latch and the hook body. All this may lead to a temptation to skip the use of the safety latch, for example by tying it permanently into the open position against the inside of the hook body with tape. Assigning a second person to assist is not very cost-effective, when the work contribution of the assistant is time-wise short, i.e. keeping the safety latch open does not usually take much time.
However, methods have been developed to keep the safety latch open without the user having to use his/her hands for it. For example, the safety latch may be provided with a kind of operating handle attached pivotably to the safety latch at a distance from its fastening end, the handle extending around the hook body and being lockable behind the hook body into a position keeping the safety latch open. A safety latch of this type is disclosed in U.S. Pat. No. 3,008,210. In this solution, however, the handle has to be separately released after the load has been detached in order to tension the safety latch again to the closed position. This releasing action may require quite a lot of strength, and if the safety latch has a powerful spring, the user may still hurt his/her hands if they for some reason get caught between the operating handle and the hook body or between the latch end of the safety latch and the hook body. Then again, if the safety latch is left or forgotten completely open after a load has been fastened and for the duration of a subsequent lifting, the safety latch is of no use. Inserting a hoist belt with one hand into the hook jaw easily rotates the hook. In many cases, handling a hoist belt with two hands prevents the hook from rotating around its vertical axis during handling.